package com.zhouhong;
/**
 * @ClassName: array-queue
 * @Description: 基于数组的循环队列
 * @Author: zhouhong
 * @Create: 2021-03-31 00:31
 **/
public class LoopQueue<E> implements  QueueInterface<E>{

    private E[] data;
    private int front, tail;
    private int size;

    public  LoopQueue(int capacity){
        data = (E[]) new Object[capacity + 1];
        front = 0;
        tail = 0;
        size = 0;
    }
    public LoopQueue(){
        this(10);
    }

    public int getCapacity(){
        return data.length - 1;
    }

    @Override
    public void enqueue(E e) {
        // 循环队列已经满了
        if ((tail + 1) % data.length == front){
            resize(getCapacity() * 2);
        }
        data[tail] = e;
        tail = (tail + 1) % data.length;
    }

    @Override
    public E dequeue() {
        if (isEmpty()){
            throw new IllegalArgumentException("循环队列不能为空");
        }
        E res = data[front];
        data[front] = null;
        front = (front + 1) % data.length;
        size --;
        if (size == getCapacity() / 4 && getCapacity() / 2 != 0){
            resize(getCapacity() / 2);
        }
        return res;
    }

    @Override
    public E getFront() {
        if (isEmpty()){
            throw new IllegalArgumentException("循环队列不能为空");
        }
        return data[front];
    }

    @Override
    public int getSize() {
        return size;
    }

    @Override
    public boolean isEmpty() {
        return front == tail;
    }

    private void resize(int newCapacity){
        E[] newData = (E[]) new Object[newCapacity + 1];
        for (int i = 0; i < size; i++) {
            newData[i] = data[(i + front) % data.length];
        }
        data = newData;
        front = 0;
        tail = size;
    }

    @Override
    public String toString() {
        StringBuilder result = new StringBuilder();
        result.append(String.format("Queue: size = %d, capacity = %d\n", size, getCapacity()));
        result.append("front [");
        for (int i = front; i != tail ; i = (i + 1) % data.length) {
            result.append(data[i]);
            if ((i + 1) % data.length != tail){
                result.append(", ");
            }
        }
        result.append("] tail");
        return result.toString();
    }

}
